¹ Biomark, Inc., 705 South 8th Street, Boise, Idaho, 83702, USA
² Washington Department of Fish and Wildife, Under A Bridge, Seattle, Washington, 00000, USA
³ Mount Hood Environmental, PO Box 4282, McCall, Idaho, 83638, USA

^✉ Correspondence: Richard A. Carmichael <Richard.Carmichael@merck.com>

Keywords: northern pikeminnow; Chinook salmon; predation; mark-recapture; bioenergetics

Introduction

The Upper Salmon River major population group (MPG) supports eight independent, extant spring/summer Chinook Salmon Oncorhynchus tshawytscha populations including Salmon River (above Redfish Lake), Valley Creek, Yankee Fork Salmon River, East Fork Salmon River, Salmon River (mainstem below Redfish), Pahsimeroi River, Lemhi River, and North Fork Salmon River (NOAA 2017). At least five of these eight populations must meet criteria set forth by McElhany et al. (2000) and ICTRT (2007) for the MPG to be considered viable and for the recovery of the Snake River Evolutionary Significant Unit (ESU). Populations within the ESU have substantial cultural value, support downriver mainstem Snake and Columbia River commercial and subsistence fisheries, and support local fisheries and economies in years with sufficient abundance. All populations within the Upper Salmon River MPG have become depleted in recent decades. Declines in survival of juvenile Chinook Salmon have been attributed to the removal of beavers from the landscape (fur trade), mining activities, river simplification, water withdrawals, logging activities, urbanization, avian predation, proliferation of non-native species (e.g., non-native coastal rainbow trout O. mykiss irideus and brook trout Salvelinus fontinalis), warming streams and rivers, and modifications to downriver migration corridors (e.g., from hydropower projects). Moreover, the abundance of returning adults are further impacted by ocean and downriver harvests, poor ocean conditions, and changes to the spawning migration corridor. Each of these factors have contributed, to varying and unknown extents, to reduced adult escapement, the primary metric used to assess population viability. In response to the decline in Chinook Salmon abundance from the myriad human activities and associated habitat degradation, action agencies have attempted to improve juvenile survival and adult spawning conditions by investing in the rehabilitation of tributary ecosystems.

Paragraph 2

One potentially important, but perhaps under-appreciated source of mortality on Chinook salmon is predation on emigrating juveniles by piscivorous fishes, including both native and non-native species. As an example,…

At this point, I’m thinking leave avian predation out of the equation, but instead include in Discussion
and keep focus on the freshwater environment
What is known about downriver (Columbia/Snake) piscivorous fish populations and potential predation on juvenile Chinook salmon?
- literature review of northern pikeminnow, smallmouth bass, other? predation on juvenile Chinook salmon, particulary from the Snake and Columbia rivers
- still stay away from avian predation

An estimated 200 million juvenile salmonids emigrate through the lower Snake and Columbia rivers, annually. Of those, approximately 16.4 million (8%) are consumed by northern pikeminnow [Beamesderfer1996]. (Peterson1994?) estimated that the annual loss of juvenile salmonids to northern pikeminnow to be 7.3% of all juvenile salmonids entering the John Day Reservoir. Additionally, 78% of these salmonids consumed near a dam were consumed when alive (Peterson1994?). Dams are known to be areas of predation, but (Ward1995?) estimated that 48% of predation is occurring away from dams in mid-reservoir areas. Most of the research has been targeted around dams and reservoirs, but there are areas functioning similar to a reservoir in the rivers upstream. One of these areas is the Deadwater Slough in the Salmon River. The Deadwater Slough is a 25.3-acre area that is unnaturally slow and deep within the Salmon River and resembles a small reservoir (Figure 3). This unnatural area has little to no cover, higher depth, and fine substrate which favor piscivorous fish predators (e.g., northern pikeminnow Ptychocheilus oregonensis, smallmouth bass Micropterus dolomieu) (Watkins2015?). Axel et al. (2015) demonstrated decreased rates of emigration and apparent survival for Sockeye Salmon Oncorhynchus nerka from Redfish Lake emigrating during the spring. Further, recent winter telemetry studies have indicated decreased transition probabilities (approximately 10% less than surrounding reaches) of juvenile Chinook salmon through Deadwater Slough during fall and winter months (Ackerman et al. 2018; Porter et al. 2019).

Spring/summer Chinook Salmon in the Upper Salmon MPG are stream-type and exhibit two distinct migration tactics; downstream rearing (DSR) and natal reach rearing (NRR) (Copeland et al. 2014). The DSR migrants leave the natal spawning area as subyearlings between June and November and typically overwinter in downstream, mainstem habitats until the following spring when they emigrate to the ocean as smolts. Alternatively, NRR migrants remain in their natal spawning areas for approximately one year after emergence until emigration to the ocean as smolts. Diversity of migratory tactics provides a mechanism for coping with adverse conditions in freshwater rearing and migration environments and buffers against catastrophic events, thereby increasing population resiliency.

The Deadwater Slough is in a reach of the Salmon River that is believed to be a historically important overwinter rearing area for DSR emigrants. Moreover, this reach is part of the migratory pathway for juvenile DSR and NRR emigrants from all eight extant populations. The slough lacks hydrological and structural features (i.e., a homogenous channel with fine substrate and little cover) that can provide essential refuge from predation. As a result, predation on juvenile Chinook salmon proximal to the Deadwater Slough has been cited as a concern for the Upper Salmon River MPG, impacting DSR migrants in the fall and NRR emigrants during the spring.

We hypothesize that increased densities of piscivorous predators in the Deadwater Slough may explain the reduced survival (or apparent survival) observed for juvenile Chinook Salmon (Ackerman et al. 2018) and Sockeye Salmon (Axel et al. 2015). In this study, we estimated the abundance of a piscivorous fish predator population in the Deadwater Slough and their potential impacts to juvenile salmon emigrants, focusing on DSR and NRR Chinook Salmon. Our objectives for the study were four-fold:

Estimate the abundance (or relative abundance) of potential predators in the Deadwater Slough during the peaks of fall (DSR) and spring (NRR) juvenile emigrations.
Document predation on juvenile Chinook Salmon during the emigration periods using gastric lavage.
Use a bioenergetics approach to estimate the total consumption of juvenile DSR and NRR Chinook salmon during defined emigration periods.
Quantify the potential impacts of estimated predation on juvenile to Chinook Salmon adult returns.

We follow with a discussion of the various assumptions that went into the mark-recapture and bioenergetics models and assessment of impacts to adult returns and how violations of some assumptions may affect overall results and inferences from the study.

Methods

Study Site

The Deadwater Slough is an approximately 1.5 kilometer section of the mainstem Salmon River located roughly 5.8 river kilometers downstream from the town of North Fork, Idaho (Figure 3). The downstream end of the slough is located at the confluence of Dump Creek and the Salmon River. Around 1897, the failure of a small mining diversion reservoir in the Dump Creek drainage resulted in an erosion event that deposited substantial amounts of sediment at the confluence of the Salmon River, thereby creating an unnaturally slow and deep section in the river, spanning approximately 30 acres and averaging 68 m width. Both northern pikeminnow Ptychocheilus oregonensis and smallmouth bass Micropterus dolomieu inhabit the slough which likely provides favorable conditions for their feeding and growth (e.g., reduced water velocity, deep channel, warmer water temperature).

Abundance of Piscivorous Fishes

Data = C/M/R and Effort

Capture methods used - We initially attempted electrofishing, snorkeling, netting, others?, but eventually settled on angling as best method for mark-recapture.
Mark-recapture - We kept the mark and recapture events close together in an attempt to use a closed population model
What are the assumptions of a closed population model?
How was sampling performed? What relevant information was captured for each fish? How/where were fish released? How was effort recorded to calculate CPUE?
Description of sampling time frame:
- Fall 2019: Goal was to estimate abundance during the peak of DSR emigration i.e., timing was done to coincide to be shortly after peak fall (DSR) emigration at the lower Lemhi River screw trap with the hopes of documenting predation. DSR are the more abundant juvenile emigration tactic.
- Fall 2020: Intent was to repeat the above, but instead during peak NRR emigration, but effort canceled due to COVID-19. Instead, sampling was re-schedule to fall when social distancing, etc. could be put in place.
- Spring 2021: Did a relative abundance effort during spring 2021. Had to reduce to a CPUE (single-week) effort due to funding constraints. However, goal was to 1) document presence during NRR outmigration and 2) estimate CPUE to provide a relative comparison to the fall efforts.

The Lincoln-Petersen estimator is below, where $M$ is the number of fish marked and returned to the population, $n$ is the number of fish caught in the second/recapture event and $m$ is the number of marked fish in the second sample.

\[ \hat{N} = \frac{(M)(n)}{(m)} \]

The Lincoln-Petersen estimator can be biased with small samples, so we also investigated the Chapman-modified Lincoln-Petersen estimator which is shown below. \[ \hat{N} = \frac{(M + 1)(n + 1)}{(m + 1)} - 1 \] The Schnabel estimator is shown below, where the $M$, $n$ and $m$ are indexed by the sampling occasion, $i$. In our example, the sampling occasions are defined as each day of sampling. This estimator does not have an associate standard error, but 95% confidence intervals can be calculated. \[ \hat{N} = \frac{\sum\limits_{i = 1}^k n_i M_i}{\left(\sum\limits_{i = 1}^k m_i \right) + 1} \] There is another estimator for this type of multiple census surveys, called the Schumacher-Eschmeyer estimator, which is based on minimizing the weighted sum of squares between the proportion of marked individuals in the sample and the unknown proportion of marked individuals in the population. It is shown below.

\[ \hat{N} = \frac{\sum\limits_{i = 1}^k n_i M^2_i}{\sum\limits_{i = 1}^k m_i M_i} \] We additionally calculated the proportional stock density (PSD) of northern pikeminnow with 300 mm total length (TL) for stock and 400 mm TL for quality. \[ PSD_{i} = 100 * \frac{FQ_{i}}{FS_{i}} \] where $FQ_{i}$ is the number of fish $\ge$ quality-length for species $i$, and $FS_{i}$ is the number of fish $\ge$ stock-length for species $i$.

Predation On Juvenile Chinook Salmon

We were interested in documenting potential consumption of juvenile Chinook Salmon by northern pikeminnow, and ideally, estimate the proportion of their diet consisting of juvenile Chinook Salmon at the time of sampling. To accomplish this, we collected stomach contents using gastric lavage as described in Foster (1977) and examined contents for the presence or absence of juvenile Chinook Salmon or other incidentals (e.g., steelhead, Sockeye Salmon, Redside Shiner, etc.), and the proportion of any stomach contents containing fish or fish parts versus non-targets (e.g., macroinvertebrates, organic matter, etc.). Stomach contents were stored in whirl-paks, preserved with 99% isopropyl alcohol, and analyzed within the following week in a controlled environment. Each sample was uniquely identified to match up with the appropriate fish record, contents were identified down to their unique composition, total weight of all content was measured as wet weight in grams, and total weight of fish content, if found, was measured in grams. Fish and fish parts were identified down to species, if possible, or categorized as unknown if unidentifiable. Throughout the sampling periods a subset of the capture individuals were sacrificed after gastric lavage to validate whether gastric lavage was successful at flushing stomach contents from the northern pikeminnow.

Bioenergetics

To estimate the impacts from northern pikeminnow on juvenile Chinook Salmon outmigrants in Deadwater Slough, we used an R-based application of Fish Bioenergetics v4.0 developed by (Deslauriers2017?). We estimated a daily rate of consumption for an individual northern pikeminnow based on predator and prey energy densities, water temperatures, and predator start and end weights. We also ran two alternative models one with a year of temperature inputs from 2019, and another with the same temperature inputs but a 10% growth in weight of the average pikeminnow at the end of the model. The average length of northern pikeminnow captured at the Deadwater Slough during our study was 370.6 mm which calculates to an average starting weight of 847 g using the FSA package ((Ogle2019?)) in R which provides a weight-length formula for northern pikeminnow sourced from (Parker1995?). Predator energy density for northern pikeminnow was available in the Bioenergetics v4.0 application and was fixed at 6,703 Joules(J)/g. Prey energy densities was taken from (Moss2016?) where they estimated juvenile Chinook Salmon at 21,500 J/g. Using these temperatures, weights, and energy inputs, we estimated a total consumption in grams for an individual norther pikeminnow within Deadwater Slough.

We ran three bioenergetic models for this study. First, we chose a 78-day period from September 1 through November 17 where we know Chinook Salmon DSR emigrants begin to enter the mainstem Salmon River from natal tributaries (e.g., Lemhi River) and begin to migrate downstream, but when temperatures are still high enough that juveniles are not yet exhibiting concealment behavior or torpor. The second model was still assuming no growth but taking the entire year into account for the model rather than the 78-day fall period. The assumption of no growth for pikeminnow was included to show what may be occurring if the population of northern pikeminnow is stable. If growther of the population is occurring, the alternative model shows how an increase of 10% body weight changes the estimates of consumption over a full year period. To estimate the number of possible Chinook Salmon that could be consumed, we assumed a weight of 12 g per individual chinook Salmon. This weight was an average from juvenile Chinook salmon emigrating past six rotary screw traps operating in the Upper Salmon above Deadwater Slough including traps in the Lemhi, Pahsimeroi, and North Fork Salmon rivers and one trap operating near the Sawtooth hatchery.

Impacts to Adult Returns

Text here…

Results

Abundance of Piscivorous Fishes

Table 1: Data summary for single census estimators. M is the number of fish caught in the first sample, marked and returned to the population. n is the number of fish caught in the second sample, and m is the number of marked fish caught in the second sample.
Sampling Event	Species	M	n	m
Fall 2019	Northern Pikeminnow	267	396	7
Fall 2020	Northern Pikeminnow	500	297	5

Table 2: Data summary for multiple census estimators. n is number of fish caught, m is the number of marked fish caught, u is the number of unmarked fish caught, and R is the number of marked fish returned to the population.
Sampling Event	Species	Date	n	m	u	R
Fall 2019	Northern Pikeminnow	2019-11-12	29	0	29	28
Fall 2019	Northern Pikeminnow	2019-11-13	146	0	146	146
Fall 2019	Northern Pikeminnow	2019-11-14	93	1	92	93
Fall 2019	Northern Pikeminnow	2019-11-19	149	2	147	132
Fall 2019	Northern Pikeminnow	2019-11-20	104	1	103	77
Fall 2019	Northern Pikeminnow	2019-11-21	143	4	139	118
Fall 2020	Northern Pikeminnow	2020-10-20	173	0	173	170
Fall 2020	Northern Pikeminnow	2020-10-21	188	1	187	187
Fall 2020	Northern Pikeminnow	2020-10-22	104	0	104	102
Fall 2020	Northern Pikeminnow	2020-10-23	41	0	41	41
Fall 2020	Northern Pikeminnow	2020-10-27	42	0	42	41
Fall 2020	Northern Pikeminnow	2020-10-28	47	1	46	46
Fall 2020	Northern Pikeminnow	2020-10-29	163	4	159	162
Fall 2020	Northern Pikeminnow	2020-10-30	45	0	45	45

Sampling Event	Estimator	N	SE	Lci	Uci
Fall 2019	Chapman	13,298	4,322.3	6,898	27,893
Fall 2019	Petersen	15,105	5,658.3	7,331	37,569
Fall 2019	Schnabel	18,732		10,057	37,851
Fall 2019	Schumacher-Eschmeyer	20,615		14,393	36,313
Fall 2020	Chapman	24,882	9,253.8	11,784	56,907
Fall 2020	Petersen	29,700	13,170.0	12,727	91,470
Fall 2020	Schnabel	37,556		18,698	82,105
Fall 2020	Schumacher-Eschmeyer	43,279		23,061	351,090

Figure 1: Estimates of abundance of northern pikeminnow using different estimators.

Figure 2: Total catch per unit effort across entire sampling event.

PSD for northern pikeminnow across all three years was 42.26% or 42.26% of fish were over the quality size classification 400 mm TL we denoted in the Methods, demonstrating a high percentage of above average size classs present within Deadwater Slough.

Predation On Juvenile Chinook Salmon

During 2019, 660 northern pikeminnow were gastric lavaged. Of those fish, 603 had empty stomachs, 57 had stomach contents, 12 had fish parts, and of those 12 with fish parts 1 MWF and 2 shiners. During the 2020 season 805 northern pikeminnow were gastric lavaged with 613 empty stomachs, 188 with stomach contents and 23 with fish parts. Out of the 23 stomachs with fish parts present 10 were unknown, 6 red sided shiner, 4 suckers, 2 sculpin, and 1 chinook. In 2021, we had 105 stomach samples with 98 being non-fish and 7 having fish or fish parts.

Bioenergetics

Over the fall time period a single northern pikeminnow is modeled to eat 61 g of fish. If we extrapolate this out to the potential effect the estimated population of xx,xxx, then xxx,xxx g of fish are being eaten each fall during the migration of juvenile Chinook salmon having the potential to consume *xxx juvenile Chinook as a discrete population.

Over the point of a whole year, a single northern pikeminnow is modeled to eat 283 g of fish and 613 g of other food types.

Impacts to Adult Returns

SAR results. Maybe a plot of multiple scenarios depending on gastric lavage results? And pop estimates if they vary in time.

Discussion

We estimated the population size of Northern Pikeminnow in the Deadwater Slough to be greater than xx,xxx during the fall emigration period for DSR Chinook Salmon. That estimate translates to a density of xxx Northern Pikeminnow per 100 m or xxx per 100 m² which is similar/more/less than estimates from elsewhere in the Columbia River (citation) where substantial Northern Pikeminnow predation impacts on salmonids have led to bounty programs aimed at reducing Northern Pikeminno abundance. The population size of Northern Pikeminnow was not directly estimated during the spring NRR Chinook salmon emigration period however, the relative abundance measured at CPUE was comparable to the fall sampling periods (update statement later). The population of Northern Pikeminnow in Deadwater Slough was estimated to consume between xx,xxx and xx,xxx juvenile Chinook Salmon during the x sampling periods and result in an estimated reduction of returning adults between xxx and x,xxx. We suggest that the habitat modifications that created the Deadwater Slough have resulted in favorable conditions for Northern Pikeminnow, including improved conditions for predation upon juvenile Chinook Salmon (add detail here). Therefore, predation by Northern Pikeminnow in the Deadwater Slough likely has a consequential impact on ESA-listed Chinook Salmon populations in the Upper Salmon River MPG.

Mark-Recapture Model

Gastric Lavage

We were able to gastric lavage the majority of fish collected including some non-predatory species. We euthanized nine northern pikeminnow for dissection to confirm that the gastric lavage was effective in removing stomach contents. Our results support the findings the previous year that dissected individuals that the dissected gastric lavage was effective in removing stomach contents ((Lott2020?)). Additionally , we found that the fish captured in trap-nets had a similar proportion of stomach content samples. Of those, 1,214 (76.2%) were completely empty, 345 (21.6%) had stomach contents, and 35 (2.2%) contained fish parts. We were able to identify juvenile shiners, a largescale sucker, sculpin, mountain whitefish, and one Chinook Salmon within stomach contents, but most samples were too digested to identify to species.

Bioenergetics

What assumptions did we make during the bioenergetics assessment? And how might violations of those assumptions change our estimate of the number of juvenile Chinook salmon consumed and resulting impacts to adult returns?

Impacts to Adult Returns

Again, what assumptions did we make here and how might violations of those assumptions change our estimate of impacts to adult returns.

Avian Predation

Although not formally assessed in this study, avian predators including Great Blue Herons Ardea herodias and Bald Eagles Haliaeetus leucocephalus are another potential source of mortality for juvenile salmon in the Deadwater Slough. The Deadwater Slough is recognized as an important bird watching and nesting area due to the riparian and backwater habitats created by the feature (Deadwater Slough - Audubon Important Bird Areas). Several piscivorous bird species have been documented using the Deadwater Slough that include the Common Mergus merganser and Hooded Lophodytes cucullatus mergansers, the Great Blue Heron, the Double-crested Cormorant Phalacrocorax auritus, and the Belted Kingfisher Megaceryle alcyon (eBird 2021). During the intial sampling event in 2019, a two-person crew walked the entire reach and surrounding and upstream areas scanning for passive integrated transponder (PIT) tags. During that informal survey, nine PIT tags were recovered near active bird nests or in an upstream anastomizing reach where herons and eagles are prevalent, suggesting that mortality may have been a result of avian predation. The PIT tag histories in PTAGIS indicate these tags were implanted into a combination of juvenile Chinook Salmon (3), Sockeye Salmon (3), and steelhead (3). Avian predation contributes a major component of the total mortality for yearling Chinook Salmon in some locations in the lower Snake River and Columbia River, particularly at hydroelectric dams and within reservoirs (Evans et al. 2012; 2016); however, we did not observe large colonies of piscivorous birds within the study area. Although there is documentation of individual Double-crested Cormorants (eBird 2021) at the Deadwater Slough, the site is not within their breeding range, rather, it is part of a migration corridor. Given the current avian species known to occupy Deadwater Slough, it is unlikely that avian predation on juvenile salmonids is comparable to elsewhere in the Columbia River basin with large piscivorous bird colonies. Nevertheless, we hypothesize that the reservoir-like conditions at the Deadwater Slough may increase the probability of avian predation on juvenile Chinook Salmon from the many piscivorous birds known to use the site. Future estimates of predation would benefit from consideration of the contribution of piscivorous avian predators.

Management Implications

We estimated that consumption of juvenile Chinook Salmon by northern pikeminnow in the Deadwater Slough potentially reduces annual adult returns by xxx - x,xxx to upriver populations. Presumably, that reduction in adult returns impacts both the ESA-listed natural populations in the Upper Salmon River MPG plus the two hatchery populations in the Upper Salmon, Pahsimeroi and Sawtooth hatcheries, which provide for recreational fishing opportunities. Fisheries managers desire increased adult returns to both aide in the recovery of natural populations as well as to provide additional harvest in recreational fisheries to boost local economies. A reduction in predation mortality at Deadwater Slough on juvenile Chinook Salmon has potential to benefit multiple upriver natural and hatchery populations, in contrast to typical tributary habitat rehabilition actions which typically benefit a single population. Moreover, the deepened, slack water conditions that favor northern pikeminnow at Deadwater Slough are indirectly the result of manmade activities i.e., the failure of a manmade mining reservoir dam. Given these reasons, it seems that Deadwater Slough could be a candidate for management or restoration actions to benefit local Chinook Salmon populations.

We see two potential management actions: 1) removing the Dump Creek delta to restore flow and 2) a local northern pikeminnow bounty program to encourage harvest of northern pikeminnow in Deadwater Slough.

Is there anything in the literature that discusses habitat preferences for pike minnow? If we speed up velocities and add some cover potentially pike minnow predation success will be lowered. Will these fish just move elsewhere?

Conclusions

We have also presented a novel modeling framework for estimating predation on native, critically endangered anadromous species which can be applied to other areas of interest. John day? Others?
The end.

Acknowledgements

The authors extent much appreciation to the many volunteers who assisted with field efforts including collaborators from Bureau of Reclamation, Idaho Department of Fish and Game, and Lemhi Regional Land Trust, among others. This manuscript benefited from reviews and contributions from colleagues at the Idaho Governor’s Office of Species Conservation, Rio Applied Science and Engineering, and from Sean Gibbs and Ben Briscoe at Mount Hood Environmental. Funding for this study was provided by the Bureau of Reclamation, Pacific Northwest Regional Office (contract No. 140R1021F0018). Special thanks to Caitlin Alcott and Inter-Fluve for their administrative support and guidance.

Literature Cited

Ackerman, M. W., G. A. Axel, R. A. Carmichael, and K. See. 2018. Movement and Distribution of Sp/Sum Chinook Salmon Pre-smolts in the Mainstem Salmon River, Pilot Study. Unpublished.

Axel, G. A., M. Peterson, C. C. Kozfkay, B. P. Sandford, M. G. Nesbit, B. J. Burke, K. E. Frick, and J. J. Lamb. 2015. Characterizing migration and survival between the Upper Salmon River Basin and Lower Granite Dam for juvenile Snake River sockeye salmon, 2014. Page 36. Fish Ecology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration and Idaho Department of Fish and Game.

Copeland, T., D. A. Venditti, and B. R. Barnett. 2014. The Importance of Juvenile Migration Tactics to Adult Recruitment in Stream-Type Chinook Salmon Populations. Transactions of the American Fisheries Society 143(6):1460–1475.

eBird. 2021. eBird: An online database of bird distribution and abundance [web application]. eBird, Cornell Lab of Ornithology, Ithaca, New York. Available: http://www.ebird.org. Accessed: November 10, 2021.

Evans, A. F., N. J. Hostetter, D. D. Roby, K. Collis, D. E. Lyons, B. P. Sandford, R. D. Ledgerwood, and S. Sebring. 2012. Systemwide Evaluation of Avian Predation on Juvenile Salmonids from the Columbia River Based on Recoveries of Passive Integrated Transponder Tags. Transactions of the American Fisheries Society 141(4):975–989.

Evans, A. F., Q. Payton, A. Turecek, B. Cramer, K. Collis, D. D. Roby, P. J. Loschl, L. Sullivan, J. Skalski, M. Weiland, and C. Dotson. 2016. Avian Predation on Juvenile Salmonids: Spatial and Temporal Analysis Based on Acoustic and Passive Integrated Transponder Tags:18.

Foster, J. R. 1977. Pulsed Gastric Lavage: An Efficient Method of Removing the Stomach Contents of Live Fish. The Progressive Fish-Culturist 39(4):166–169. Taylor & Francis.

ICTRT. 2007. Viability criteria for application to Interior Columbia Basin salmonid ESUs. National Marine Fisheries Service, Northwest Fisheries Science Center.

McElhany, P., M. H. Ruckelshaus, M. J. Ford, T. C. Wainwright, and E. P. Bjorkstedt. 2000. Viable salmonid populations and the recovery of evolutionarily significant units. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-42.:156.

NOAA. 2017, November. ESA Recovery Plan for Snake River Spring/Summer Chinook Salmon (Oncorhynchus Tshawytscha) & Snake River Basin Steelehad (Oncorhynchus Mykiss).

Porter, N. J., M. W. Ackerman, T. Mackey, G. A. Axel, and K. E. See. 2019. Movement and Distribution of Chinook Salmon Presmolts in the Mainstem Salmon River, 2018/2019 Annual Report. Page 47. Biomark, Inc. - Applied Biological Services and Fish Ecology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration.

Tables

Figures

$Map of the Deadwater Slough study area. The high-resolution orthoimage portion directly surrounding the Deadwater Slough was generated from aerial images taken by a drone. The red polygon indicates the reach characterized by unnaturally slow water velocities and a deepened channel. The location of the Dump Creek delta is indicated.$

Figure 3: Map of the Deadwater Slough study area. The high-resolution orthoimage portion directly surrounding the Deadwater Slough was generated from aerial images taken by a drone. The red polygon indicates the reach characterized by unnaturally slow water velocities and a deepened channel. The location of the Dump Creek delta is indicated.

Colophon

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The current Git commit details are:

#> Local:    main C:/Git/DeadwaterPaper
#> Remote:   main @ origin (https://github.com/BiomarkABS/DeadwaterPaper.git)
#> Head:     [19eef1d] 2021-11-16: Merge branch 'main' of https://github.com/BiomarkABS/DeadwaterPaper

Northern Pikeminnow Predation on Juvenile Chinook Salmon and Potential Impacts to Local Populations

Richard A. Carmichael^1,✉, Nicholas J. Porter¹, Kevin E. See^1,2, Michael S. Hall¹, Tara E. Blackman³, and Michael W. Ackerman^1,3

16 November, 2021

Introduction

Methods

Study Site

Abundance of Piscivorous Fishes

Predation On Juvenile Chinook Salmon

Bioenergetics

Impacts to Adult Returns

Results

Abundance of Piscivorous Fishes

Predation On Juvenile Chinook Salmon

Bioenergetics

Impacts to Adult Returns

Discussion

Mark-Recapture Model

Gastric Lavage

Bioenergetics

Impacts to Adult Returns

Avian Predation

Management Implications

Conclusions

Acknowledgements

Literature Cited

Tables

Figures

Colophon

Northern Pikeminnow Predation on Juvenile Chinook Salmon and Potential Impacts to Local Populations

Richard A. Carmichael1,✉, Nicholas J. Porter1, Kevin E. See1,2, Michael S. Hall1, Tara E. Blackman3, and Michael W. Ackerman1,3

16 November, 2021

Introduction

Methods

Study Site

Abundance of Piscivorous Fishes

Predation On Juvenile Chinook Salmon

Bioenergetics

Impacts to Adult Returns

Results

Abundance of Piscivorous Fishes

Predation On Juvenile Chinook Salmon

Bioenergetics

Impacts to Adult Returns

Discussion

Mark-Recapture Model

Gastric Lavage

Bioenergetics

Impacts to Adult Returns

Avian Predation

Management Implications

Conclusions

Acknowledgements

Literature Cited

Tables

Figures

Colophon

Richard A. Carmichael^1,✉, Nicholas J. Porter¹, Kevin E. See^1,2, Michael S. Hall¹, Tara E. Blackman³, and Michael W. Ackerman^1,3